Sensors for detecting leaking hydrocarbons, such as gasoline or hydrocarbon based solvents and other products are well known. Such detectors or sensors are generally used on storage tanks gasoline stations or pipelines containing such hydrocarbon products.
The known sensors generally operate on the principle of an open to closed electrical circuit. The principle as follows: a sensor is formed of a pair of conductors which form an open circuit. A change in the electrical status occurs in the presence of a hydrocarbon, causing the circuit to be closed (become electrically connected). The leakage is detected as a result of the detection of the completed circuit.
Variations on this principle are well known. For example, U.S. Pat. No. 4,926,165 contains a swellable material, which when it swells, causes an electrical connection between the two conductors, thus completing the circuit. Likewise, U.S. Pat. No. 4,972,179 uses three conductors to form a wheatstone bridge circuit when the second and third conductors are short circuited by the presence of a liquid.
The complexity of the known devices leads to high cost. Further, most of these detectors are not reusable, thereby increasing their cost and shortening their useful life span. Perhaps the biggest disadvantages with the existing sensors are their sensitivity and their selectivity. Most sensors send false signals in the presence of contaminated ground water (such as ground water containing salts or other non-organic contaminants). Additionally, the sensitivity of the sensors varies widely. Some, such as those which rely upon the swelling of one layer to contact a second layer so as to close a circuit, require an adversely high concentration of hydrocarbons to be present before completing a circuit. These problems make quick, reliable and repeatable detection of leaks difficult, if not impossible.
The present invention overcomes the problems encountered in the known systems. The object of the present invention is to provide a sensor for detecting the presence of hydrocarbons without the generation of false signals, or the need for high concentrations of hydrocarbons and with the ability to provide repetitive, reliable detection.